The nature of the visual representation for words has been fiercely debated for over 150 y. We used direct brain stimulation, pre-and postsurgical behavioral measures, and intracranial electroencephalography to provide support for, and elaborate upon, the visual word form hypothesis. This hypothesis states that activity in the left midfusiform gyrus (lmFG) reflects visually organized information about words and word parts. In patients with electrodes placed directly in their lmFG, we found that disrupting lmFG activity through stimulation, and later surgical resection in one of the patients, led to impaired perception of whole words and letters. Furthermore, using machine-learning methods to analyze the electrophysiological data from these electrodes, we found that information contained in early lmFG activity was consistent with an orthographic similarity space. Finally, the lmFG contributed to at least two distinguishable stages of word processing, an early stage that reflects gist-level visual representation sensitive to orthographic statistics, and a later stage that reflects more precise representation sufficient for the individuation of orthographic word forms. These results provide strong support for the visual word form hypothesis and demonstrate that across time the lmFG is involved in multiple stages of orthographic representation. (1), whereas Wernicke firmly rejected that notion, proposing that reading only necessitates representations of visual letters that feed forward into the language system (2). Similarly, the modern debate revolves around whether there is a visual word form system that becomes specialized for the representation of orthographic knowledge (e.g., the visual forms of letter combinations, morphemes, and whole words) (1, 3, 4). One side of the debate is characterized by the view that the brain possesses a visual word form area that is "a major, reproducible site of orthographic knowledge" (5), whereas the other side disavows any need for reading-specific visual specialization, arguing instead for neurons that are "general purpose analyzers of visual forms" (6).The visual word form hypothesis has attracted great scrutiny because the historical novelty of reading makes it highly unlikely that evolution has created a brain system specialized for reading; this places the analysis of visual word forms in stark contrast to other processes that are thought to have specialized neural systems, such as social, verbal language, or emotional processes, which can be seen in our evolutionary ancestors. Thus, testing the word form hypothesis is critical not only for understanding the neural basis of reading, but also for understanding how the brain organizes information that must be learned through extensive experience and for which we have no evolutionary bias.Advances in neuroimaging and lesion mapping have focused the modern debate surrounding the visual word form hypothesis on the left midfusiform gyrus (lmFG). This focus reflects widespread agreement that the lmFG region plays a critical role ...

Perception reflects not only sensory inputs, but also the endogenous state when these inputs enter the brain. Prior studies show that endogenous neural states influence stimulus processing through non-specific, global mechanisms, such as spontaneous fluctuations of arousal. It is unclear if endogenous activity influences circuit and stimulus-specific processing and behavior as well. Here we use intracranial recordings from 30 pre-surgical epilepsy patients to show that patterns of endogenous activity are related to the strength of trial-by-trial neural tuning in different visual category-selective neural circuits. The same aspects of the endogenous activity that relate to tuning in a particular neural circuit also correlate to behavioral reaction times only for stimuli from the category that circuit is selective for. These results suggest that endogenous activity can modulate neural tuning and influence behavior in a circuit- and stimulus-specific manner, reflecting a potential mechanism by which endogenous neural states facilitate and bias perception.

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